The invention relates to a feed pump with a driven impeller which rotates in a pump casing and has in its end faces at least one ring of guide blades delimiting blade chambers and in which the blade chambers have an inflow region and an outflow region for the medium to be fed, and with at least one part-annular channel which is arranged in the region of the guide blades in the pump casing and which forms with the blade chambers a feed chamber from an inlet channel to an outlet channel, the contour of the blade chambers being formed by at least one radius with an origin within the feed chamber.
Such feed pumps are often used for feeding fuel in a fuel tank or for feeding washing fluid in a shield washing system of a motor vehicle and are known from practice. The known feed pump has a ring of blade chambers in each of the two end faces of the impeller. The blade chambers are delimited in the radially outer direction by a straight wall arranged perpendicularly to the end faces of the impeller. The contour of the blade chambers which points in the radially inner direction of the impeller is generated by a radius. The origin of the radius is located on the center line arranged perpendicularly to the end faces of the impeller. This origin is at the same time the origin of a second radius forming the part-annular channel.
One disadvantage of the known feed pump is that it generates turbulences in the medium to be fed. These turbulences lead to the feed pump having low efficiency. Moreover, in the case of media which are near the boiling point, such as, for example, hot gasoline fuel, there is the risk that vapor bubbles will be formed within the feed chamber. The vapor bubbles lead to a sharp reduction in the volume flow fed by the feed pump.
The problem on which the invention is based is to design a feed pump of the type initially mentioned, in such a way that it has as high an efficiency as possible and reliably prevents the formation of vapor bubbles.
This problem is solved, according to the invention, in that, as seen from the blade chamber contour determined by the radius, the origin of the radius is located in the region opposite a center line of the blade chamber, said center line running perpendicularly to the end face of the impeller.
By virtue of this design, the blade chamber has, in its region formed by the radius, a contour which ascends at a very low inclination. A circulation flow in the feed chamber alternates between the impeller and the pump casing via this low-inclination contour. Since the circulation flow undergoes only slight deflection in this region, the risk of turbulences is kept particularly low. The formation of vapor bubbles is also avoided as a result.
According to an advantageous development of the invention, the impeller can be manufactured cost-effectively if the origins of a plurality of radii for blade chamber contours opposite one another are located on a common plane within the impeller, said plane running parallel to the end face of the impeller.
Turbulences often occur in the region in which the circulation flow alternates between the blade chamber and the part-annular channel. According to another advantageous development of the invention, the circulation flow set in turbulence here can be calmed again quickly if, from the plane running parallel to the end face of the impeller as far as the end face, the blade chambers have, in their regions adjacent to the guide blades, boundaries guided perpendicularly to the end face of the impeller.
According to another advantageous development of the invention, the impeller has simply constructed blade chambers and can therefore be manufactured particularly cost-effectively if the origins of two radii generating in each case contours opposite one another are arranged mirror-symmetrically to the center line of the blade chamber. As a result, the center line can be designed as a bisecting line for the contour pointing toward the center of the impeller and for the contour pointing away from the center of the impeller.
The feed pump according to the invention has particularly high efficiency if the distance of the origins of the radii from the center line is approximately the same amount as their distance from the end face.
As in the known feed pump, blade chambers arranged opposite one another could be connected to one another in a radially outer region of the impeller. However, a contribution to a further increase in the efficiency of the feed pump according to the invention is made if blade chambers arranged opposite one another mirror-symmetrically in the two end faces of the impeller are connected to one another solely in the region of the center line. The circulation flow can thereby flow from one feed chamber over into the other feed chamber with particularly low turbulences. Moreover, the risk of the formation of vapor bubbles is likewise kept particularly low as a result.